2025/10/03 by Gao, Zijian, Shan, Qianxue, Zhou, Ziqin +2
#FOS: Physical sciences #Medical Physics (physics.med-ph)
paper · doi:10.48550/arxiv.2510.02847
Purpose: Inhomogeneous magnetization transfer (ihMT) effect reflects dipolar order with a dipolar relaxation time (T1D), specific to motion-restricted macromolecules. We aim to quantify T1D using spin-lock MRI implemented with a novel rotary-echo sequence. Methods: In proposed method, we defined a relaxation rate Rdosl that is specific to dipolar order and obtained as the difference of dual-frequency R1rhodual relaxation and single-frequency R1rhosingle relaxation. A novel rotary-echo spin-lock sequence was developed to enable dual-frequency acquisition. We derive the framework to estimate T1D from Rdosl under macromolecular pool fraction (MPF) map constraints. The proposed approach was validated via Bloch-McConnell-Provotorov simulation, phantom studies, and in-vivo white matter studies on a 3T scanner. Results: Simulations demonstrated that Rdosl exhibits an approximately linear relationship with T1D. Phantom experiments showed robust ihMT contrast in Rdosl and confirmed the feasibility and reliability of T1D quantification via Rdosl. In vivo white-matter studies further supported the clinical potential of this T1D mapping approach. Conclusion: We propose a novel, clinical feasible method for T1D quantification based on spin-lock MRI. This method requires substantially fewer contrast-prepared images compared to the conventional T1D quantification approach. This technique provides a promising pathway for robust MPF and T1D quantification in a single rapid scan with reduced confounds.